(1) Field of the Invention
The present invention relates to methods used to fabricate a color image sensor cell, and more specifically to a method used to protect a bond pad structure from the processes used to define the color filter elements of the color sensor cell.
(2) Description of Prior Art
Color image sensor cells are usually comprised with metal structures, used as cell electrodes for picture elements, and used as bonding pads, which are needed for electrical connection with external circuits. In addition the color image sensor cell is comprised of color filter elements formed on a dielectric layer, overlying the cell electrodes, and bonding pad structures. However the process of forming the color filter elements can degrade the bonding pad, if the top surface of the bonding pad is exposed to the processes used to define the overlying color filter elements. Degradation of the bonding pad, via staining, occurring as a result of a wet developer step performed during the development cycle of the color filter elements, can result in yield loss due to poor wire bonds, or reliability failures in terms of wire bond failures occurring during the lifetime of the color image sensor cell.
This invention will describe a process sequence for forming a color image sensor cell in which the top surface of bonding pad is protected during the processes used to form the color filter elements, thus preventing exposure of the top surface of the bonding pad to the developer solution, used to define the color filter elements. Prior art, such as Harada et al, in U.S. Pat. No. 4,783,691, describe a method of forming a color image sensor, however that prior art does not detail the opening made to the bonding pad, in terms of etchant used, whereas this present invention features a final dry etching procedure, for exposure of the bonding pad, while the bonding pad remains protected during the color filter image sensor cell definition.
It is an object of this invention to fabricate a color image sensor cell, comprised with picture element, cell electrodes, bonding pad structures, and color filter elements.
It is another object of this invention to deposit a dielectric layer on the underlying bonding pad, prior to the formation and definition of the color filter elements, to protect the surface of the bonding pad during a wet developer cycle used for the definition of the color filter elements.
It is yet another object of this invention to define the contact opening to bond pad structure using a final dry etching procedure.
In accordance with the present invention a process for forming a color image sensor cell, featuring the use of a dielectric layer, used to protect the surface of a wire bond pad from wet developer procedures, used to define the color filter elements of the cell, is described. After formation of metal structures such as cell electrode, picture elements, and a wire bond pad, a passivation layer, comprised of an underlying layer of silicon oxide, and an overlying layer of silicon nitride, is deposited. A first planarization layer of photoresist is next applied. Color filter elements are then formed on the top surface of the first planarization layer, with the top surface of the wire bond pad protected by the passivation layer, during the fabrication of the color filter elements. After application of a second planarization layer, the portion of the contact hole, overlying the bond pad structure is defined via photolithographic exposure and wet development procedures, with the opening to the wire bond pad then finalized via a dry etching procedure, removing the portion of exposed passivation layer.